The continuous shrinking in dimensions of electronic devices utilized in ULSI (ultra large scale integration) circuits in recent years has resulted in increasing the resistance of the BEOL metallization as well as increasing the capacitance of the intralayer and interlayer dielectric. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (k) insulators and particularly those with k significantly lower than silicon oxide are needed to reduce the capacitances. Dielectric materials (i.e., dielectrics) that have low k values are commercially available. One such commercially available material, for example, is polytetrafluoroethylene (“PTFE”), which has a dielectric constant of about 2.0. Most commercially available dielectric materials however are not thermally stable when exposed to temperatures above 300° C. Integration of low k dielectrics in present ULSI chips requires a thermal stability of at least 400° C.
The low k materials that have been considered for applications in ULSI devices include polymers containing atoms of Si, C, O and H, such as methylsiloxane, methylsilsesquioxanes, and other organic and inorganic polymers. For instance, a paper (N. Hacker et al. “Properties of new low dielectric constant spin-on silicon oxide based dielectrics” Mat. Res. Soc. Symp. Proc. 476 (1997): 25) describes materials that appear to satisfy the thermal stability requirement, even though some of these materials propagate cracks easily when reaching thicknesses needed for integration in an interconnect structure when films are prepared by a spin-on technique. Furthermore, these prior art precursor materials are high cost and prohibitive for use in mass production. Moreover, most of the fabrication steps of very-large-scale-integration (“VLSI”) and ULSI chips are carried out by plasma enhanced chemical or physical vapor deposition techniques.
The ability to fabricate a low k material by a plasma enhanced chemical vapor deposition (PECVD) technique using previously installed and available processing equipment will thus simplify its integration in the manufacturing process, reduce manufacturing cost, and create less hazardous waste. U.S. Pat. Nos. 6,147,009 and 6,497,963 describe a low dielectric constant material consisting of atoms of Si, C, O and H having a dielectric constant not more than 3.6 and which exhibits very low crack propagation velocities.
U.S. Pat. Nos. 6,312,793, 6,441,491, 6,541,398 and 6,479,110 B2 describe a multiphase low k dielectric material that consists of a matrix phase composed of atoms of Si, C, O and H and another phase composed mainly of C and H. The dielectric materials disclosed in the foregoing patents have a dielectric constant of not more than 3.2.
U.S. Pat. No. 6,437,443 describes a low k dielectric material that has two or more phases wherein the first phase is formed of a SiCOH material. The low k dielectric material is provided by reacting a first precursor gas containing atoms of Si, C, O, and H and at least a second precursor gas containing mainly atoms of C, H, and optionally F, N and O in a plasma enhanced chemical vapor deposition chamber.
Despite the numerous disclosures of methods of fabricating low k SiCOH dielectric films, the prior art SiCOH films contain a high content of C atoms (typically about 10-20 atomic % or greater) that increase the leakage currents of the device containing the SiCOH film. The increase in leakage current, in turn, degrades the insulating property of the film and therefore adversely effects the films reliability. Thus, there is a need for providing SiCOH films that have improved leakage current using a method that does not effect the dielectric constant and/or the reliability of the SiCOH film.